Thin oxide (e.g., SiO2) and oxynitride (e.g., SiOxNy) layers are often used as dielectric layers at the Si surface of an integrated circuit. This is in part because of excellent electrical properties of the oxide and oxynitride layers, including high electron mobility and low electron trap densities. Semiconductor transistor technology is currently requiring oxide and oxynitride gate dielectric layers for conventional gate dielectric applications that are less than about 10-15 angstrom (A) thick, or as thin as 5-7 A for use as interface layers with high-dielectric constant materials (also referred to herein as high-k materials).
A native oxide layer that is typically a few angstrom thick, forms easily on clean Si surfaces, even at room temperature and atmospheric pressure. An oxide layer with a desired thickness that is larger than the native oxide thickness, can be grown through the native oxide layer, but usually the thickness uniformity and quality of the oxide layer is poor across the entire Si substrate.
Alternatively, the native oxide (or the chemical oxide) can be removed from Si surface prior to growing a new oxide layer. The native oxide layer can, for example, be removed using liquid baths containing dilute hydrofluoric acid (HF) or by using HF gas phase etching. A new oxide layer can then be re-grown on the clean Si surface by conventional thermal oxidation, but the initial oxidation can proceed quickly and result in poor thickness uniformity and inadequate electrical properties. For ultra-thin (<20 A) oxide layers used in transistor technologies, the leakage current is dominated by the tunneling current.